Hybrid vehicle and control method for hybrid vehicle

Abstract

A hybrid vehicle includes an engine, a motor generator, a main battery, a DC-DC converter, a sub-battery, a starter, and an electronic control unit. The DC-DC converter is a bidirectional converter configured to convert a voltage of electric power from the sub-battery and output the electric power to the motor generator. The electronic control unit is configured to control the DC-DC converter such that the sub-battery outputs electric power to the motor generator when a first available electrical energy of the main battery is smaller than a required electrical energy at the time when the engine is started with the use of the motor generator.

What is claimed is: 
     
       1. A hybrid vehicle comprising:
 an engine; 
 a motor generator coupled to the engine; 
 a main battery configured to supply electric power to the motor generator; 
 a DC-DC converter configured to convert a voltage of electric power from the main battery and the motor generator, and output the electric power; 
 a sub-battery configured to be supplied with electric power from the DC-DC converter; 
 a starter configured to start the engine when supplied with direct-current power from the sub-battery; and 
 an electronic control unit configured to start the engine with the use of any one of the starter and the motor generator, 
 the DC-DC converter being a bidirectional converter configured to convert a voltage of electric power from the sub-battery and output the electric power to the motor generator, and 
 the electronic control unit being configured to control the DC-DC converter such that the sub-battery outputs electric power to the motor generator when a first available electrical energy of the main battery is smaller than a required electrical energy at a time when the engine is started with the use of the motor generator, the required electrical energy being set as a value larger than or equal to a minimum electrical energy required to start the engine with the use of the motor generator. 
 
     
     
       2. The hybrid vehicle according to  claim 1 , wherein
 the electronic control unit is configured to, when the first available electrical energy of the main battery is larger than or equal to the required electrical energy, control the DC-DC converter such that the main battery outputs electric power to the sub-battery, and start the engine with the use of the motor generator. 
 
     
     
       3. The hybrid vehicle according to  claim 2 , wherein
 the electronic control unit is configured to, when the first available electrical energy of the main battery is larger than or equal to the required electrical energy, control the DC-DC converter such that an electrical energy that is output from the main battery to the sub-battery reduces as the first available electrical energy of the main battery approaches the required electrical energy. 
 
     
     
       4. The hybrid vehicle according to  claim 1 , wherein:
 the electronic control unit is configured to calculate a second available electrical energy available to be supplied from the sub-battery to the motor generator; 
 the electronic control unit is configured to, when the first available electrical energy of the main battery is larger than or equal to a value obtained by subtracting the second available electrical energy from the required electrical energy and is smaller than the required electrical energy, control the DC-DC converter such that the sub-battery outputs electric power to the motor generator, and start the engine with the use of the motor generator; and 
 the electronic control unit is configured to, when the first available electrical energy of the main battery is smaller than the value obtained by subtracting the second available electrical energy from the required electrical energy, control the DC-DC converter such that the main battery outputs electric power to the sub-battery, and start the engine with the use of the starter. 
 
     
     
       5. The hybrid vehicle according to  claim 4 , wherein
 the electronic control unit is configured to calculate the second available electrical energy such that the second available electrical energy increases as a state of charge of the sub-battery increases. 
 
     
     
       6. The hybrid vehicle according to  claim 1 , further comprising
 a temperature sensor configured to detect a coolant temperature of the engine, wherein 
 the electronic control unit is configured to calculate the required electrical energy such that the required electrical energy increases as the coolant temperature of the engine decreases. 
 
     
     
       7. A control method for a hybrid vehicle, wherein the hybrid vehicle includes an engine, a motor generator coupled to the engine, a main battery configured to supply electric power to the motor generator, a DC-DC converter configured to convert a voltage of electric power from the main battery and the motor generator and output the electric power, a sub-battery configured to be supplied with electric power from the DC-DC converter, a starter configured to start the engine when supplied with direct-current power from the sub-battery, and an electronic control unit configured to start the engine with the use of any one of the starter and the motor generator, the DC-DC converter being a bidirectional converter configured to convert a voltage of electric power from the sub-battery and output the electric power to the motor generator,
 the control method comprising
 controlling, by the electronic control unit, the DC-DC converter such that the sub-battery outputs electric power to the motor generator when a first available electrical energy of the main battery is smaller than a required electrical energy at a time when the engine is started with the use of the motor generator, the required electrical energy being set as a value larger than or equal to a minimum electrical energy required to start the engine with the use of the motor generator.